This project is designed to study the history of changes in the concept of fever from the eighteenth to the twentieth centuries. We plan to trace the successive definition of the various diseases all of which were once called fever, and shall describe the effects of changes in the concept of fever on the practice of medicine. Although in the eighteenth and nineteenth centuries physicians tended to share a common fund of medical ideas drawn from the medical literature, when they attempted to observe disease independently, they were influenced inevitably by the nature of the diseases which formed their immediate medical experience. Thus the perception of fever by physicians, and the concepts of fever they formed, might vary as a result of variations in the geographical distribution of disease, or as a result of differences in living conditions among different social classes. Physicians' experience of disease might also reflect large scale movements of people brought about by such factors as trade, industrialization, war, or famine. Because of the great prevalence of fevers in the eighteenth and nineteenth centuries this study will illustrate the many factors which influenced concepts of fever, and therefore of the nature of disease, as medicine emerged into the modern period. It will be a study of the evolution of scientific concepts of disease within medicine.